I don't know if its relevant here to comment, but I am really left out of ideas. I have an old beloved Hercules bike with a sachs internal hub that is tottally damaged. Apparently I used a used SG 7C25 hub to replace it. When i realised that it is not working properly the last one I took the internal mechanism of a SG7C16 hub and replaced it in the shell of the SG7C25. Still not working. I have 5 instead of 7 gears (after 5 there are no changes at all) and along with the axle the dust cup turns also!! Are the mechanisms compatible? does anybody know? I ve read that basically you can replace anything more or less in nexus hubs as soon as they are both with/without coaster brake. They really look the same (the mechanisms inside) I tested so many times! any ideas about the problem? Why no changes whatsoever after the fifth gear? or where to look for solutions! Thanks in advance.